The broad objective is to further our understanding of the subprocesses involved in human verbal and visuo-spatial short-term (working) memory. The primary aim is to ascertain whether verbal short-term memory consists solely of a phonologically based articulatory rehearsal loop, or whether the rehearsal of verbal information is also actively supported by lexical and semantic codes. One view holds that lexical-semantic codes are not involved in rehearsal of verbal information in short-term memory, but they do contribute to memory performance by priming the long-term memory system. Then the primed codes support the subsequent retrieval process. The other view argues that lexical-semantic activation helps sustain information in short-term memory during rehearsal. It has been difficult to resolve this issue with behavioral data alone, since they reflect a combination of storage, rehearsal and retrieval operations, and any resolution depends upon identifying processes that are specific to storage and rehearsal operations. Our approach will be to utilize neuroelectric activity, measured by event-related brain potentials (ERPs) recorded from human scalp, to index brain processes specific to storage and rehearsal of information in short-term memory. We will test the hypothesis that lexical-semantic information is actively involved in verbal short-term memory by attempting to demonstrate that ERP indices of short-term memory storage and rehearsal are influenced by the lexical-semantic content of material to be remembered. The second aim is to test the hypothesis that visuo-spatial short-term memory consists of anatomically distinct subsystems for rehearsing object-feature and spatial information. We will seek evidence for this hypothesis by assessing any differences in the scalp topographies of ERP indices of rehearsal when object and spatial information are maintained in visuo-spatial short-term memory. Memory deficits are a key aspect of many cognitive-neurological impairments. Clinical utilization of ERPs for diagnosis of non-cognitive neurological disorders is now routine, and there are data which further indicate that cognitive impairments due to different types of neurological disorders have differential effect's upon ERPs. As the extent and precision of our knowledge of how ERPs index cognitive activity increases, ERPs could become a vital, non-invasive tool in the diagnosis of cognitive impairments and design of therapies.